Primrose - Ludwigia uruguayensis
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Uruguayan water primrose is a herbaceous perennial and has two different
growth forms: in one form glabrous or sparsely pubescent stems grow horizontally
over the soil or water and produce roots at nodes and, often, white, spongy
roots. These roots are feathery but stiff. Leaves are mostly glabrous,
alternate, petiolate, but so congested at the tip to appear to be in rosettes.
Leaf shape varies from suborbicular to obovate to spatulate with a round
apex and base. Plants do not flower when only floating leaves are present.
In the other growth form, plants elongate from the rosette stage (described
above) and grow above the surface of the water. The stems are pubescent
and erect, up to 1 m tall. The leaves are pubescent, variable in shape
from lanceolate to elliptic and acute at both ends. Upper leaves may be
subsessile or sessile, the lower leaves petiolate. Flowers are solitary
from the upper leaf axils and on stalks 2 to 3 cm long. Sepals and petals
are 5, sometimes 6, the petals bright yellow. The fruit is a pubescent
capsule with many seeds.
In general appearance and growth form, L. uruguayensis is similar
to L. peploides (Kunth) Raven. The erect flowering stems, and
long, shaggy hairs along the stem and on the leaves of L. uruguayensis
are characters that can be used to separate it from L. peploides
which typically is glabrous to sparsely pubescent and has flowering stems
that are weakly ascending.
Ludwigia uruguayensis is found in marshes, along marshy shores,
in swamps, ponds and lakes, sloughs, ditches, irrigation and drainage
canals. The horizontal stems may extend several meters from the shoreline
into shallow water areas and form large floating mats. After senescence
in the fall months, small leaves are produced along the stem and remain
until regrowth begins in late winter or early spring (Aulbach-Smith &
de Kozlowski 1996). Seeds may aid in species dispersion. Large colonies
can prevent small boat navigation and recreational use of shoreline areas.
Links to more information
Website, video, and graphics by Rob Nelson
For more information on this plant or management please contact US Army Corp of Engineers
Uruguayan Primrose Video
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